Micro injection molding machine

ABSTRACT

A molding machine for molding microparts containing between 0.001 to 3.5 cubic centimeters of plastic shot volume includes a plasticizing portion operatively connected to an injection portion and a mold portion. A valve member is provided to open and close the connection between the plasticizing portion and the injection portion. A linear motor member is associated with the injection portion to permit molding times of 0.01 seconds at pressures up to about 100,000 psi during injection of the molten plastic into the mold portion.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a novel injection moldingmachine for molding microparts containing a plastic shot volume ofbetween about 0.001 to 3.5 cubic centimeters. Specifically, the microinjection molding machine utilizes pneumatic cylinder or cylinders forthe plasticization and delivery of the resin material to the injectionportion of the molding machine. A linear motor drives the injectionportion to inject the resin material through the nozzle into the moldcavity to complete the injection molding of the micropart.

[0002] Injection molding processes are well known and have beendeveloped for molding plastic parts. These processes generally involvemelting plastic or resin pellets by feeding the pellets through a heatedscrew barrel utilizing a rotating screw. The heated barrel together withthe heat supplied by the shear of the plastic pellets heats the resinpellets above their melting point. The screw is supported axially with aload and as the molten plastic moves to the front of the screw, thebuildup in pressure forces the screw backwards until a desired volume ofplastic has been developed in front of the screw. At this point, therotating screw is stopped and the molten plastic is injected by movingthe screw forward to force plastic through the nozzle into the cooledmold cavity to provide the desired molded part. The mold cavity iscooled and the injected plastic is fixed to the desired shape of thepart. Such known technology and operations require that the forwardmotion of the screw must fill the mold cavity to obtain a good quality,dense molded part.

[0003] The prior art processes for injection molding are adequate formolding normal size parts utilizing shot sizes in excess of 3.5 to 5.0cubic centimeters; however, when the microparts require very small shotvolumes of less than 3.5 cubic centimeters there are significantproblems with existing processes and technology. For example, the screwor auger means used to transport the plastic or resin pellets must beminiaturized in diameter to accept the resin pellets. If the screw istoo large, it will contain many volumes of plastic relative to the partbeing molded. In such a situation, the plastic remaining heated in thebarrel after each molding cycle degrades over time when held at thismelting temperature. However, if the screw or auger is miniaturized andthe screw flight depths are smaller than the pellet size, problems existconcerning accepting the pellets and feeding the resin plastic orpellets into the auger to allow compression and melting of the plastic.Although resin pellet diameter sizes are normally in the range of 2.5 mmor greater, miniature pellets of about 1.25 mm exist. However, the screwinjection processes are limited to injection moldings of shot sizeslarger than 3.5 cubic centimeters, even when the plastic pellet size isabout 1.25 mm.

[0004] Furthermore, it should be pointed out that the smallest availablescrew or auger today is 14 mm in diameter and such auger devices areunable to precisely meter and maintain the accuracy of the moldedplastic below the resolution limit of the screw stroke injectionmachine.

[0005] Additionally, existing injection molding processes for moldingmicroparts are unsatisfactory because the microparts often require athin wall thickness ranging from about 0.025 to 0.30 mm. To force andinject the plastic into these thin walled microparts without freezing,very high pressures and short injection times are required. Existingconventional molding machines generate approximately 25,000 psi pressureand require a 0.5 second injection time for molding shot sizes greaterthan 3.5 cubic centimeters.

[0006] However, if it is desired to injection mold shot sizes or volumescontaining less than about 3.5 cubic centimeters, the necessary forcerequired approaches 100,000 psi and a 0.01 second injection time whenthe wall thicknesses of the micropart is approximately 0.05 mm. Thus,existing prior art molding machines and processes are incapable ofmolding plastic shot sizes or volumes approaching 3.5 cubic centimetersor less to provide uniform molded microparts without large variations inpart dimensions from shot to shot.

[0007] Accordingly, to injection mold microparts the injection moldingmachine must create a high injection pressure and possess controlledinjection speed profiles substantially less than 0.5 seconds. Also,existing technology and processes utilize hydraulic pressures to createthe injection pressures and injection speed profiles. However, hydraulicfluids are not readily compatible with clean room facilities. Thus, theinjection molding of medical grade devices and related microparts isseverally limited with existing technology.

[0008] One attempt to overcome the problems of these known injectionmolding machines and processes, has suggested that the injection machineinclude a system wherein the heated plastic is plasticized and thenintroduced into the front of an injection plunger. However, suchmachines have poor quality control over the filling of the plastic intothe mold cavity because they utilize or require air cylinders to drivethe injection plunger, a structure and mechanism which cannot accuratelycontrol the speed of injection. More importantly, such injection moldingmachines cannot stop the injection process as the mold cavity is filledexcept by the increase in pressure buildup during the molding process.The control of the molding process by measuring the increase in pressureyields a high variability in the molded parts, a result which isunsatisfactory for most molded operations. U.S. Pat. No. 5,380,187describes a molding machine comprised of a combination of a screw orauger to mix, heat and plasticize the plastic or resin material fordeposit before an injection plunger to accomplish the filling process.However, such devices are limited to molding shot volumes ofsubstantially greater than 3.5 cubic centimeters and are unsatisfactoryfor molding thin-walled microparts.

SUMMARY OF THE INVENTION

[0009] It is one object of the present invention to provide a novelinjection molding machine for molding microparts.

[0010] It is another object of the present invention to provide aninjection molding machine for use in molding microparts which overcomesthe deficiencies of prior art injection molding machines.

[0011] It is still another object of the present invention to provide anovel injection molding machine for molding microparts which utilizeplastic shot volumes of between about 0.001 to 3.5 cubic centimeters.

[0012] It is yet another object of the present invention to provide amicropart injection molding machine which is capable of high pressure ata very high speed during the injection phase while preventing back flowinto and past the injection cylinder portion of the micropart injectionmolding machine.

[0013] It is a further object of the present invention to provide anovel injection molding machine for microparts which is comprised of aplasticizing portion and an injection portion which permits theutilization of plastic shot volumes of between about 0.001 to 3.5 cubiccentimeters.

[0014] Also, it is an object of the present invention to provide a novelmicro injection molding machine which includes an injection portiondriven by a linear motor for precise positioning and control of the flowof molten plastic into the mold cavity to mold the micropart.

[0015] Still, another object of the present invention is to provide anovel micro injection molding machine having precise centerline controlof the injection plunger, nozzle and mold to maintain precise alignmentof the resin flow channel resulting therefrom to the precise dimensionof about less than 0.1 mm without complex realignment with each moldchange.

[0016] Yet another object of the present invention is the design of amicro injection molding machine which utilizes a support ledge on theheated cylinder block that is on the centerline of the mold, injectionnozzle, resin flow channel and injection cylinder which accommodatestemperature changes of the heating block while maintaining thecenterline of the molding machine constant.

[0017] Lastly, another object of the present invention is to provide aninjection portion of a molding machine which is adapted to readilyreceive and accommodate various sized injection cylinders and injectionpins to provide various plastic shot volumes of between about 0.001 to3.5 cubic centimeters to mold the desired sized micropart.

[0018] The present invention is directed to an injection molding machinefor molding microparts. The injection molding machine is comprised of aplasticizing portion, an injector plunger portion and a mold portion.The plasticizing portion softens and delivers the molten plastic orresin to the injection portion of the molding machine. The plasticizingportion includes a heated cylinder block surrounding or enclosing aplasticizing chamber and a screw member which meters the plastic orresin pellets into the plasticization chamber. A plasticizing plungerengages the molten plastic within the chamber. As the plastic melts, theplunger is sized to permit trapped air to exhaust between the plungerand the cylinder chamber wall. When the plastic or resin material iscompletely melted, the plastic is forced by the plasticizing aircylinder plunger past an opened valve member which separates theplasticizing portion from the injection portion into the resin flowchannel of the injection portion.

[0019] The injection portion of the molding machine includes aninjection cylinder which is positioned and secured within the cylinderblock in axial alignment with the resin flow channel which cooperateswith the nozzle to permit plastic to be injected into the mold. Theinjection portion is maintained on the centerline of the mold. Aprecision fitted injection pin member is fitted within the bore of theinjection cylinder and is maintained in very close tolerance withrespect to the bore, within the range of about 0.012 mm or less. Thisprecision fitting of the injection pin within the bore of the injectioncylinder as well as the utilization of a linear motor engaging theinjection pin permits the application of high pressures at very highspeeds during the injection phase of the molten resin through the resinflow channel and nozzle into the mold portion. Also, the precisionfitting prevents back flow between the injection pin and the cylinderbore during the molding process. The valve member, positioned betweenthe injection portion and the plasticizing portion is closed during theinjection process to prevent back flow of the resin material into thelower pressure capacity plasticizing cylinder. The valve member is atapered valve which is, preferably, powered by an air cylinder. Thevalve member is positioned inside the plasticizing cylinder block and ismaintained at the proper uniform plastic melt temperature.

[0020] When the heated plastic or resin material is forced by theplasticizing cylinder into the resin flow channel and the injectioncylinder, the valve member is closed and the injection pin is drivenforwardly to pressure the flow of heated plastic through the nozzle andsprue into the closed mold cavity.

[0021] The injection pin is driven by an electric motor means. The termelectric motor means may be used to describe a rotary motor coupled to aball screw device which converts the rotary motion to a linear motion.However, it is a preferred embodiment of the present invention that theelectric motor means is a linear motor which directly provides linearmotion to the injection pin. The term “linear motor” is used to describea motor that is electrically driven in a linearly motion rather than ina rotary motion. One type of linear motor useful in the presentinvention is a linear servo or stepper motor manufactured and sold byTrilogy Linear Motor, Webster, Tex. The linear motor provides a linearmotion which engages and controls the speed and pressure engaging theinjection pin.

[0022] The electronic control of the linear motor provides for the veryhigh speed movement of the injection pin while maintaining precisioncontrol and location of the injection pin. The position of the injectionpin is continuously monitored and feed to the electronic control systemby a linear measuring device, such as an LVDT. The injection pin isengaged and pushed by the linear motor, but is not necessarily directlycoupled to the linear motor. If desired, the elimination of directcoupling between the injection pin and linear motor avoids the necessityof precise alignment with respect to the injection pin and the linearmotor. The forward axial movement of the injection pin within the resinflow channel injects between about 0.001 to 3.5 cubic centimeters ofplastic shot volume into the mold, as desired.

[0023] After completion of the mold cycle, the injection pin is axiallymoved rearwardly under load as the valve member is opened and moltenplastic from the plasticizing cylinder enters the resin flow channel toforce the injection pin rearwardly from the mold portion. The flow ofplastic into the resin flow channel returns the injection pin during thereloading cycle of a predetermined shot volume of molten plastic fromthe plasticizing portion into the injection portion.

[0024] After the flow of molten resin into the resin channel, known asthe preparation of a predetermined shot volume of molten plastic, themold portion is moved axially away from the nozzle and the mold isopened to permit ejection of the molded micropart from the moldingcavity. Thereafter, the valve member is closed and the mold portion ismoved axially to engage the nozzle to repeat the molding cycle for thepredetermined shot volume.

[0025] As set forth above, the injection nozzle cooperates with theinjection pin to facilitate injection of the heated resin or plasticmaterial through the sprue opening into the mold cavity. The mold cavityis designed such that the molded micropart may be readily removed fromthe mold cavity by ejection pins or suction after each cycle ofoperation. By utilizing plastic or resin flow channels of about 0.5 to6.0 mm in diameter, plastic shot volumes of between about 0.001 to 3.5cubic centimeters may readily be achieved. Moreover, because of thereduced size of the plastic flow channel, the number of parts that canbe molded, utilizing the molten plastic or resin contained within theplasticizing chamber, is reduced thereby insuring maximum moldingefficiency without degradation of the plastic or resin material betweenloadings of the pellets.

[0026] Other and additional objects of the present invention will beapparent from the following description and claims that are illustratedin the accompanying drawings which, by way of their illustration, show apreferred embodiment of the present invention and the principles thereofand what is now considered to be the best mode contemplating in applyingthose principles. Other embodiments of the present invention employingthe same or equivalent principles may be used and structural changes maybe made as desired by those skilled in the art without departing fromthe present invention and the scope of the appended claims.

DESCRIPTION OF THE DRAWINGS

[0027] The foregoing description or other characteristics, objects,features and advantages of the present invention will become moreapparent upon consideration of the following detailed description,having reference to the accompanying drawings wherein;

[0028]FIG. 1 is a cross-sectional view of the injection molding machineillustrating the loading of plastic or resin pellets into theplasticizing portion of the injection molding machine in accordance withthe present invention;

[0029]FIG. 2 is a cross-sectional view of the injection molding machineillustrating the melting of the plastic or resin pellets in theplasticizing portion and the filling of the injection portion with apredetermined shot volume of molten plastic in accordance with thepresent invention;

[0030]FIG. 3 is a cross-sectional view of the injection molding machineillustrating the injection of plastic or resin material through theresin flow channel and nozzle into the mold by movement of the linearelectric motor in accordance with the present invention;

[0031]FIG. 4 is a cross-sectional view of the injection molding machineillustrating axial movement of the mold portion from the injectionportion and the opening of the mold to eject the molded micropart inaccordance with the present invention;

[0032]FIG. 5 is an enlarged fragmentary view illustrating the valvemember closed between the plasticizing portion and the injection portionof the injection molding machine in accordance with the presentinvention;

[0033]FIG. 6 is an enlarged fragmentary view illustrating the valvemember opened between the plasticizing portion and the injection portionto permit the flow of a predetermined shot volume of melted plasticresin material into the injection portion in accordance with the presentinvention;

[0034]FIG. 7 is an enlarged fragmentary view illustrating the positionof the injection pin during filling of the resin flow channel withmolten plastic or resin material from the plasticizing portion inaccordance with the present invention; and

[0035]FIG. 8 is an enlarged fragmentary view illustrating thepositioning of a valve member between the plasticizing portion and theinjection portion in accordance with a further embodiment of the presentinvention.

DETAILED DESCRIPTION

[0036] Referring now to the drawings wherein like numerals have beenused throughout the several views to designate the same or similarparts, the present invention is directed to a injection molding machinefor molding microparts. The microparts generally possess wall thicknessranging between about 0.025 to 0.3 mm. As shown in FIGS. 1-4 of thedrawings, the micro injection molding machine 10 is comprised of aplasticizing portion 12, an injection portion 14 and a mold portion 11.The plasticizing portion 12 is adapted to soften and control feed moltenplastic or resin into the injection portion of the molding machine. Theinjection molding machine 10 includes a heated cylinder block 16comprised of an upper portion 17 and a lower portion 18 which areintegral to one another. The upper and lower portions of the cylinderblock 16 preferably include heater holes 20 therein, best shown in FIGS.5 and 6. The heating holes are positioned throughout the block 16 andare adapted to receive electrical cartridge heaters 21 therein toprovide uniform heating of the cylindrical block.

[0037] The plasticizing portion 12 includes a spiral screw or augerfeeder member 22 which is driven for clockwise rotation by a steppermotor (not shown). The upper end 23 of the spiral screw member isadapted to receive the plastic or resin pellets 24 from a hopper 25containing a supply of plastic pellets. The plasticizing portion 12further includes a plasticizing air cylinder 26 which drives aplasticizing plunger 27 within the plasticizing chamber or bore 13,positioned within the heated cylinder block 16 and containing the heatedplastic pellets. The bore 13 is adapted to receive the plastic or resinpellets 24 from the spiral screw member 22, the position as shown inFIG. 1. The plasticizing plunger 27 cooperates with the bore 13 in theheated cylinder block 16 to compress and heat the plastic or resinpellets to a liquid state, the position as shown in FIG. 2. Theplasticizing plunger 27 is sized with respect to the bore 13 to permittrapped air to escape past the plunger and bore wall during thecompression and heating of the plastic pellets.

[0038] Also, as shown in FIGS. 1 and 7, a conduit 29 exits the bore 13and communicates with the resin flow channel 32 of the injection portion14 of the injection molding machine 10. Located within the conduit 29 isa high pressure valve member 31 which is operable between an open andclosed position, as shown in FIGS. 5 and 6. The conduit 29 is adapted tointersect the resin flow channel 32 to deliver and fill the injectionchannel with melted plastic or resin material, as will hereinafter bedescribed.

[0039] The injection portion 14 of the molding machine 10 is comprisedof a resin flow channel 32, an injection cylinder 33 and an injectionpin 34 which is engageable with a push pin 35 coupled to a linear drivemeans or motor means 36, best shown in FIGS. 1-4 and 7. The injectioncylinder 33 is removably mounted to a bore 37 positioned between theupper portion 17 and lower portion 18 of the cylinder block 16. Theinjection cylinder 33 includes a bore 38 extending the length thereof(FIG. 7) which defines the resin flow channel 32 therein and which isadapted to receive injection pin 34 for back and forth movement therein.The resin flow channel 32 is axially aligned with a nozzle 40 whichengages a sprue 41 in mold member 44 to permit injection of the moltenplastic or resin material through the sprue into the mold, best shown inFIG. 4. If necessary, coil heaters 42 may be provided about the cylinderblock where the resin flow channel engages the nozzle 40 to facilitateand maintain the plastic or resin material in a molten state. The coilheater is shown in FIGS. 1-4.

[0040] The injection pin member 34 is adapted to be received within thebore 38 of the injection cylinder 33 and to maintain a very closetolerance with respect to the bore within the range of about 0.012 mm orless. This precision fitting of the-injection pin within the injectioncylinder permits for the application of high pressures at very highspeeds during the injection phase while preventing backflow of moltenresin between the injection pin and the injection cylinder 33 during theinjection operation. As shown in FIG. 5, the valve member 31, positionedin the conduit 29 of the plasticizing portion 12, is closed during theinjection step (FIG. 3) to prevent backflow of the resin material intothe lower pressure capacity plasticizing cylinder. As shown in FIGS. 5and 6, the valve member 31 is a tapered valve which is powered by an aircylinder 39. The valve member 31 is positioned inside the heatedcylinder block and is maintained at a proper uniform plastic melttemperature.

[0041] In another embodiment of the present invention, the valve member31 is positioned concentrically with the plasticizing cylinder 26 andplunger 27 to predeterminely control the flow of molten plastic throughconduit 29 from the plasticizing portion to the injection portion. InFIG. 8, the tapered end 30 of the valve member 31 is structurallyarranged to engage the entrance to conduit 29 to block the flow ofmolten plastic into the injection portion during the injection step(FIG. 3) and to prevent backflow of the resin material into the pressurecapacity plasticizing cylinder.

[0042] The process of melting the plastic and filling the injectionportion is shown in FIG. 2. The melted plastic resin pellets 13 arecompressed by the plasticizing plunger 27 and valve member 31 is opened,as shown in FIGS. 6 and 8, the plasticizing plunger 27 forces the heatedplastic or resin material to flow into the resin flow channel 32 and theinjection cylinder 33 of the injection portion 14. This fills the resinflow channel, the position as shown in FIG. 2 and illustrated in FIG. 7.

[0043] The plasticizing plunger 27 is moved into the chamber or bore 13in the upper portion 17 by an air cylinder 26. The cylinder block 16,surrounding the plasticizing plunger and chamber, is heated to theproper melting and injection processing temperature for the particularplastic or resin being molded. Generally, this temperature is betweenabout 350° to 650° F. This heating is accomplished by the electricalcartridge heaters 21 which are inserted into the heating holes 20. Theheaters are preferred to be positioned within the cylinder block at anorientation which is positioned axially with respect to the injectioncylinder and resin flow channel. The force acting upon the plasticizingplunger 27 by the plasticizing air cylinder 26 and the heating resultingfrom the electrical cartridge heaters, facilitates melting of theplastic or resin pellets within the chamber or bore 13.

[0044] The valve member 31, positioned either in conduit 29 (FIGS. 1-6)or associated with conduit 29 (FIG. 8), and which is located between theresin flow channel and injection cylinder and the plasticizing chamberbore 13, is opened while the nozzle is maintained against the moldmember 44 and sprue 41. The valve member 31 is moved between the openand closed position by air cylinder 39 or by a concentric mountedcylinder, not shown in FIG. 8. During the period of time valve member 31is open, the injection portion is receiving and filled with meltedplastic and the nozzle 44 is positioned against the mold while theplastic part previously molded is cooling. This prevents melted plasticfrom exiting the nozzle 42 into the mold during the filling step.

[0045] A linear motor 36 controls the motion of the injection pin 34.During filling of the injection portion with plastic, a small load orpressure against the injection pin is maintained by the linear motor 36.Because a greater pressure is applied to the melted plastic in theplasticizing chamber by the plasticizing plunger during filling, themolten plastic entering the injection portion 14 pushes back theinjector pin 34 away from the nozzle 40, the position of the flowchannel arrow in FIG. 7. This forcing of the injector pin and linearmotor away from the nozzle aids in preventing voids from forming in themolten plastic contained in the plasticizing chamber or bore 13. Also,the engagement of the injection pin with the linear motor provides forthe predetermined control of the required shot volume for the part to bemolded. As the injection pin is forced axially rearwardly within theinjection cylinder, a linear position encoder sensor feed back to thelinear motor controller stops the injection pin at a predeterminedlocation. Because the plastic is held under pressure as the injectionpin moves axially rearwardly from the nozzle, the consistency of theplastic shot volume within the resin flow channel for subsequent moldingof the next micropart is properly and predeterminely controlled. Whenthe linear motor 36 reaches the proper position for the desired shotvolume to be injected through the resin flow channel, nozzle and sprueinto the mold, the linear motor is stopped and the load on theplasticizing cylinder is removed. Then, the valve member 31 is closed(FIG. 5) to remove the load on the plasticizing cylinder. Thereafter,the linear motor 36 moves axially rearwardly from the injection cylinderapproximately 1 mm to relieve pressure on the melt in front of theinjection pin.

[0046] As shown in FIG. 4, after the filling of the shot volume into theinjection portion and the completion of the injection of plastic intothe mold (FIG. 3), the mold members 44 and 45 are moved axially from thenozzle 40 and opened with respect to one another. During opening of themold cavity, an ejector or lifter pin 43 or a suction hose (not shown)is applied to remove the molded micropart 50 from the molded cavity. Thenozzle 40 is maintained during this period of time a distance from thecold mold to prevent cooling of the nozzle and the subsequent hardeningof the molten plastic or resin material contained in the nozzle. Themold members are coupled together in axially aligned relationship andare axially moved relative to the nozzle by mold air cylinder 47.

[0047] When the mold is closed and axially moved to engage the nozzle,the injection pin is in the rearward position. The engagement of themold against the nozzle by air cylinder 47 prevents leakage of plasticbetween the nozzle 40 and sprue 41. Plastic is then injected into thecavity of the mold by actuating the electric motor means 30 to drive theejector pin forward.

[0048] The term “electric motor means” may be used to describe a rotarymotor coupled to a ball screw device which converts the rotary motion toa linear motion. However, it is a preferred embodiment of the presentinvention that the electric motor means is a linear motor 36 whichdirectly provides linear motion to the injection pin 34. The term“linear motor” is used to describe a motor that is electrically drivenin a linearly motion rather than in a rotary motion. One type of linearmotor useful in the present invention is a linear servo or stepper motormanufactured and sold by Trilogy Linear Motor, Webster, Tex. The linearmotor provides a linear motion which engages and controls the speed andpressure engaging the injection pin.

[0049] In order to achieve a high quality molded micropart, the controlof the filling of the mold and the pressure maintained as the plasticfreezes is very important. Typically, during the first portion of thefilling the mold cavity with plastic, the linear motor 36 moves thepiston forward at a preset speed independent of the pressure developedin the plastic. This needs to be at a very high speed (up to 125cm/second velocity) for small, thin-walled microparts. At high injectionspeeds, the shear in the plastic material causes the viscosity of theplastic to decrease. This reduction in viscosity permits the machine tofill-thin-wall thicknesses before the plastic freezes. Wall thicknessbetween 0.025 and 0.30 mm is achieved in the molded micropart. Thelinear motor speed can be controlled with a servo drive to change thevelocity of the motor at predetermined steps during the filling stage.This is required when complex geometry microparts are molded because itis desirable to have a constant flow front of plastic as the mold isfilled.

[0050] When the mold cavity is nearly filled, on the order of 95 percentfilled, the injection motion is switched from a velocity control to aload or plastic pressure control. This is accomplished by sensing theposition of the injection pin 34 with a linear encoder and when thepredetermined position where the mold cavity is nearly filled isreached, the control system switches to a pressure control. Then, thepressure applied to the injected plastic is controlled by time stepscorrelated to different values. Typically, initially a higher pressureand then a lower pressure is desired. This permits plastic from theinjection cylinder to flow into the thin-walled micropart as it coolsand shrinks.

[0051] The linear motor or rotary motor coupled to a ball screw deviceare ideally suited for molding microparts because of their control ofvelocity, position and load from a single servo controller. These typesof motors are capable of applying upwards of 100,000 psi and achievingan injection time of 0.01 second when a molded micropart having a wallthickness of about 0.05 mm is desired. Also, these type of motorsprovides the ability to start and stop very quickly as required for thesmall shot size volume of plastic in accordance with the presentinvention. After the plastic is injected into the mold and the holdingpressure time completed, the mold cools to freeze the molten plastic.While this cooling is being accomplished, the molding process repeatsthe step of filling the injection portion with molten plastic andejecting the molded part, as previously described.

[0052] The present injection molding machine 10 utilizes air cylindersto drive the movement of the plasticizing plunger and to drive the axialmovement of the mold portion with respect to the injection portion. Theinjection pin movement is accomplished utilizing a linear motor toprovide high speed and high pressure during injection. Such use of aircylinders and electric motor means facilitates a clean room atmosphereto permit molding of all types of microparts, for medical and theelectronic fields.

[0053] Additionally, the positioning of the injection cylinder,injection pin, resin flow channel, the nozzle and mold at the centerline52 (FIGS. 5 and 6) of the heated cylinder block 16, preventsmisalignment of the various parts as the temperature of the componentschange. This centerline positioning reduces the dimensional differencesbetween the various parts to less than 0.1 mm. This enhanced position isfacilitated by mounting the heated cylinder block 16, containing theinjection cylinder, injection pin, resin flow channel and nozzle as onecenterline position on the molding machine frame 52, (FIGS. 5-6) andensuring the axial alignment and cooperation with the mold portion 11.

We claims:
 1. An injection molding machine for molding micropartscontaining a plastic shot volume of between about 0.001 to 3.5 cubiccentimeters, including in combination: a mold portion axially movablerelative to the molding machine between an open and closed position,said mold portion including a cavity plate member, a core plate memberand ejector means to remove the molded micropart from said mold portion;a plasticizing portion adapted to receive and melt plastic material,said plastic portion including a heated cylinder block having a chamberand a cooperating plunger operatively moveable into and out of saidchamber; an injection portion adapted to receive a predetermined shotvolume of plastic from said plasticizing portion, said injection portionincluding an axially aligned injection pin, a resin flow channel, anozzle and an injection cylinder, with said injection pin being axiallymoveable within said injection cylinder between an at-rest position andan extended position wherein said predetermined shot volume of plasticis injected through said resin flow channel, said nozzle and into themold portion to mold the micropart; a conduit positioned between saidplasticizing portion and said injection portion to permit the flow ofmelted plastic material from said plasticizing portion to said injectionportion; valve means associated with said conduit and operable betweenan open position wherein a predetermined shot volume of melted plasticflows into said injection portion to position said injection pin at saidat rest position and a closed position wherein said melted plastic insaid plasticizing portion is isolated from said injection portion duringmovement of said injection pin from said at-rest position to saidextended position; and electric motor means engageable with saidinjection pin to axially move the same from said at-rest position tosaid extended position to inject the molten plastic into said moldportion.
 2. The injection molding machine in accordance with claim 1,wherein said electric motor means is a linear motor which moves saidinjection pin at a speed of 500 cm/seconds or less.
 3. The injectionmolding machine in accordance with claim 1, wherein said heated cylinderblock of said plasticizing portion is maintained at a temperaturebetween about 350° to 650° F.
 4. The injection molding machine inaccordance with claim 1, wherein said valve means is a valve memberstructurally positioned perpendicularly with respect to said conduit andoperable between said open position and said close position.
 5. Theinjection molding machine in accordance with claim 1, wherein said valvemeans is valve member concentrically positioned with respect to saidcooperating plunger.
 6. The injection molding machine in accordance withclaim 1, wherein said conduit means extends between said chamber in saidplasticizing portion to said resin flow channel in said injectionportion.
 7. The injection molding machine in accordance with claim 1,wherein said axial centerline control of said mold portion with respectto said injection portion to about 0.1 mm or less.
 8. The injectionmolding machine in accordance with claim 1, wherein the predeterminedshot volume received by said injection portion is between about 0.01 to2.0 cubic centimeters.
 9. The injection molding machine in accordancewith claim 1, wherein said tolerance between said injection pin and saidinjection cylinder is within the range of about 0.012 mm or less. 10.The injection molding machine in accordance with claim 1, wherein saidresin flow channel has a diameter of about 0.5 to 6.0 mm.
 11. Theinjection molding machine in accordance with claim 1, when the wallthickness of the molded micropart is between about 0.025 to 0.3 mm andsaid injection time for the movement of the injection between saidat-rest and said extended position is between about 0.01 to 0.5 seconds.12. The injection molding machine in accordance with claim 1, whereinthe plastic pressure engageable with said injection pin is between about5,000 to 100,000 psi.
 13. A method of molding microparts utilizing amolding machine having a plasticizing portion, an injection portion anda mold portion, including the steps of: plasticizing resin material inthe plasticizing portion; filling the injection portion with apredetermined plastic shot volume of between about 0.001 to 3.5 cubiccentimeters of and the plasticized resin material from the plasticizingportion; and injecting said predetermined plastic shot volume into themold portion to complete the molding of the micropart.
 14. The method inaccordance with claim 13 further including the step of depositing apredetermined amount of resin material in the plasticizing portion priorto plasticizing of the resin material.
 15. The method in accordance withclaim 14 wherein said resin material is in the form of pellets.
 16. Themethod in accordance with claim 15 where said resin pellets range issize from about 1 to 3 mm.
 17. The method in accordance with claim 13wherein the step of injecting is completed between the time of about0.01 to 0.5 seconds.
 18. The method in accordance with claim 13 whereinthe step of injecting occurs at a plastic pressure of between about50,000 to 100,000 psi.
 19. In an injection molding machine for moldingmicroparts containing a plastic shot volume of between about 0.001 to3.5 cubic centimeters, the injection molding machine including a moldportion and an injection portion adapted to receive a predetermined shotvolume of plastic, with the injection portion including an axiallyaligned injection pin, a resin flow channel and a nozzle, with theinjection pin being axially moveable between an at-rest position and anextended position wherein the predetermined shot volume of plastic isinjected through the resin flow channel, the nozzle and into the moldportion to mold the micropart, the improvement comprising: a linearmotor means engageable with the injection portion to inject the moltenplastic into the mold portion.